The disclosure relates generally to sensor network, and more specifically to optical linked sensor network in a wearable electronic device such as a head mounted display (HMD).
A wearable electronic device may include numerous sensors to support different applications of the device. For example, wearable virtual-reality (VR) systems, augmented-reality (AR) systems, and mixed reality (MR) systems may include numerous image sensors. The image sensors can be used to generate physical image data of a physical environment in which a user is located. The physical image data can be provided to a processor operating a simultaneous localization and mapping (SLAM) algorithm to track, for example, a location of the user, an orientation of the HMD, and/or a path of movement of the user in the physical environment. The image sensors can also be used to generate physical image data including stereo depth information for measuring a distance between the user and an object in the physical environment. The image sensors can also be configured as a near-infrared (NIR) sensor. An illuminator may project a pattern of NIR light into the eyeballs of the user. The internal structures of the eyeballs (e.g., the pupils) may generate a reflective pattern from the NIR light. The image sensors can capture images of the reflective pattern, and provide the images to the processor to track the movement of the eyeballs of the user to determine a gaze point of the user. Based on these physical image data, the processor may determine a location and/or a movement of the user, a relative location of the user with respect to an object, a gazing direction of the user, etc. Based on this information, the VR/AR/MR system can generate and update, for example, virtual image data for displaying to the user via the near-eye display, audio data for outputting to the user via a speaker, etc., to provide an interactive experience to the user.
The industry has adopted various serial interface standards, such as the specifications provided by Mobile Industry Processor Interface (MIPI), for data transmission between devices. For example, MIPI specification defines a set of standardized interfaces (e.g., Camera Serial Interface (CSI)) for connecting between devices (e.g., between an imaging device and a processing device). The specification defines a set of physical layers including, for example, M-PHY, D-PHY, and C-PHY, for providing physical connection between the imaging device and a processing device (e.g., an application processor) for transmission of data, as well as a set of protocol layers for processing of the data (e.g., pixel-byte conversion, error detection and correction, etc.). The standardized physical layers (e.g., M-PHY, D-PHY, and C-PHY) are typically implemented as point-to-point interconnects. To provide connections between multiple imaging devices to a processing device, each imaging device may have a dedicated interconnect with the processing device. Each dedicated interconnect may include one or more data lanes for transmitting sensor data. The data lanes are typically metal wires or traces to transmit electrical signals representing the sensor data.
Although MIPI interfaces provide good performance, implementing the point-to-point MIPI physical layers for a sensor network comprising multiple sensors may be challenging, especially for a sensor network in a wearable device. To provide a dedicated interconnect between each of the sensors and a processor, a large number of electrical wires as well as input-output (I/O) interface circuitries may be needed. The electrical wires can take up substantial space at least because each of these electrical wires needs to be shielded, or otherwise be spaced apart by a certain distance, to mitigate crosstalk between the wires as they are carrying high speed signals typically at 1 GHz or above. Moreover, large signal power may be needed to overcome the resistance and capacitance of the electrical wires, which increases the power consumption by the I/O interface circuitries. The space and power taken up by the interconnects further increase when multiple data lanes are included for each dedicated interconnect. Given that a wearable device typically has a small form factor and provides very limited space for electrical wires and I/O interface circuitries, and that the wearable device needs to operate with low power, it becomes very challenging to MIPI physical layers for a sensor network in a wearable device.
Accordingly, there is a need for a sensor network which supports high speed transmission of sensor data from multiple sensors, and which occupies a small area and consumes low power.